The Dark Tower Wiki

Alt. Cover for vol.3 showing Roland and Eddie upon the plains of the River Barony

The River Barony is a Barony in Mid-world  located close to the city of Lud, in fact it appears that Lud is on the border of this Barony and The Waste Lands

It is noted as a land of great rolling plains. The River Send  cuts right through the barony and runs close to Lud. The Great Western Woods are North-West of the Barony.  The Bear Beam cuts right through the barony, south east towards the dark tower, following an old road.

During the third volume of the dark tower novel, Roland and his Ka-tet travel through the River Barony on their quest in which we learn much abot the peoples and history of the barony. 

During the days of AuntTalthia's (The leader of the last functioning town in the barony; River Crossing) Great-Great-Grandparents was still a functioning Barony with some semblance of government. The main economy relied on trade between different towns in the barony along the Grand Road, specifically the buffalo trade. According to the towspeople of River Crossing there was also apparently a castle that the population paid tribute to. If this is so, this settlement was likely the seat of this Mid-world barony.